1. Field of the Invention
The invention pertains to a stator for an electrical machine having a stator yoke, coils arranged on the stator yoke, and linking conductors have terminal elements which are each electrically connected to two ends of two respective coils.
2. Description of the Related Art
Known stators for electrical machines have a stator yoke with a number of stator teeth, which carry the electrical winding in the form of, for example, individually wound stator coils of insulated wire. The two ends of each coil are assigned to individual strands and are connected to each other in a predetermined manner by common linking conductors. In the case of a three-phase machine, the stator has three strands and thus at least three linking conductors, each of which is supplied with current with a phase offset of 120°. The linking conductors are wired to a switch box so that the electrical machine can be connected to a power source.
U.S. Pat. No. 6,369,473 discloses a stator for an electrical machine in which the wiring arrangement has electrically insulated linking conductors which are concentric with respect to each other. The terminals which accept the ends of the stator coils are in the form of projections extending from the linking conductors. For each coil end, a separate terminal projection is provided, and as a result of the radial staggering of the linking conductors thus realized here, the connecting points are also in different radial positions. The electrical connections can be realized here by a joining technique such as welding or soldering and/or by simply winding the wire around the terminal projection. The linking conductors are supported against each other and against the stator by interposed strips of insulating material.
Producing welded or soldered connections is highly labor-intensive and therefore expensive. There is also the disadvantage that the process heat introduced during the production of the connections can lead to damage to the insulation between the linking conductors and to the insulation on the winding wires in the area of the coils. As a result, undesirable electrical short-circuits can develop very quickly; these negatively affect the operation of the electrical machine and can even lead to its failure. Damage to the insulation provided between the linking conductors can also interfere with the stability with which the linking conductors are held in position. If they are no longer held in position reliably, they can no longer operate reliably either. Vibrations which can occur during the operation of the electrical machine or which are imposed on it from the outside lead to alternating mechanical loads on the electrical connections of the machine, which can come loose within a very short time. The wrapping of the terminal extensions represents a typical manual process, furthermore, which stands in the way of increasing the efficiency with which stators of this type can be manufactured. Because of the relatively large number of coil ends, there is also considerable danger that they will be connected incorrectly when the stator coils are being connected, that is, that they will be assigned incorrectly to their intended linking conductors. Even if great care is taken, it is still impossible to be 100% certain that all of the connections are made properly during the production of these stators.
U.S. Pat. No. 6,707,186 describes a stator of the general type in question with a wiring arrangement in which the linking conductors are arranged radially with respect to each other and have axially projecting terminals at predetermined positions for establishing connections with the ends of the stator coils. Receiving elements are formed on the winding bodies of the stator coils. The number of receiving elements present at each end of the coil is equal to the number of linking conductors. To establish the desired electrical contact, a coil end is first passed through all of the receiving elements, and then, by introducing one of the terminals between the associated coil end and the linking conductor, an electrical clamping-type of connection is formed. As an alternative to the forming of projecting terminals on the linking conductors, separate plug contacts can also be provided on them, each of which is then inserted into a receiving element to form a clamping-type of connection with an end of a coil.
In the case of a wiring arrangement with three linking conductors, this means that, although the coil ends must first be cut to length for all of the receiving elements, two of the three receiving elements per coil end are not used and remain unoccupied. When the linking conductors are arranged radially as described here, furthermore, the width of the unit is increased in the axial direction, because only the axially projecting terminals fit into the receiving elements, not the linking conductors themselves. This also results in the disadvantage that the linking conductors are mounted on the stator in such a way that they are not protected against vibrations or environmental influences.